Effect of epicardial or biventricular pacing to prolong QT interval and increase transmural dispersion of repolarization: Does resynchronization therapy pose a risk for patients predisposed to long QT or torsade de pointes?

The present study examined pacing site-dependent changes in QT interval and transmural dispersion of repolarization (TDR) and their potential role in the development of torsade de pointes (TdP). In humans, the QT interval, JT interval, and TDR were measured in 29 patients with heart failure during right ventricular endocardial pacing (RVEndoP), biventricular pacing (BiVP), and left ventricular epicardial pacing (LVEpiP). In animal experiments, pacing site--dependent changes in ventricular repolarization were examined with a rabbit left ventricular wedge preparation in which action potentials from endocardium and epicardium could be simultaneously recorded with a transmural ECG. In humans, LVEpiP and BiVP led to significant QT and JT prolongation. LVEpiP also enhanced TDR. Frequent R-on-T extrasystoles generated by BiVP and LVEpiP but completely inhibited by RVEndoP occurred in 4 patients, of whom 1 developed multiple episodes of nonsustained polymorphic ventricular tachycardia and another suffered incessant TdP. In rabbit experiments, switching from endocardial to epicardial pacing produced a net increase in QT interval and TDR by 17+/-5 and 22+/-5 ms, respectively (n=6, P